Vagus nerve stimulation (VNS) recently emerged as a potential progression-preventing and treatment option for congestive heart failure (CHF) patients. Experimental data have demonstrated that stimulation of the vagus nerve at the cervical level is able to reverse ventricular remodeling of the failing heart. There is also evidence that increasing parasympathetic activity may stimulate the production of nitric oxide, and reduce the devastating inflammatory process involved in heart failure. Present VNS devices for CHF involve an implanted nerve cuff electrode that connects via wires to an implantable pulse generator (IPG) in the patient's chest. In some devices, a standard pacemaker sensing lead in the ventricle provides cardiac sensing for synchronous delivery of VNS pulses in the cardiac refractory period, although other devices operate asynchronously to the cardiac cycle. CHF treatment via stimulation of both the right and left vagus nerves is known.
To reduce side effects when treating CHF, it is desirable to selectively stimulate a vagus nerve region with a majority of parasympathetic cardiac fibers, while minimizing the possible stimulation of large-diameter fibers that innervate the pharynx and the larynx.
U.S. Pat. No. 5,199,430 describes use of a nerve cuff electrode and quasi-trapezoidal (QT) pulses to selectively initiate action potentials adjacent to a central electrode, and to block the propagation of action potentials adjacent to the end electrodes along the larger-diameter nerve fibers, but not the smaller-diameter nerve fibers.
U.S. Pat. No. 7,389,145 describes a specific electrical stimulus waveform that can be applied to block nerve activity. It consists of a first sub-threshold cathodic phase immediately followed by an anodic phase, i.e., when the cathodic current reaches zero, the pulse is reverted with a non-zero amplitude. This biphasic pulse is repeated continuously, and the amplitude may be increased to block other smaller-diameter fibers as desired.
US Patent Appl'n Publ'n. 2010/0191311 describes the use of a nerve cuff electrode and two stimulation trains, a low-frequency train and a high-frequency one, delivered either using the same or different electrodes. The low frequency train can be used to recruit the desired cardiac fibers for treatment while the activity of certain nerve branches (for example, those innervating the larynx or pharynx), are blocked via the high-frequency train. An identical technique, showing reverse nerve fiber recruitment, was disclosed by Baratta et al. in 1989, although not in the vagus nerve (Baratta et al. “Orderly Stimulation of Skeletal Muscle Motor Units with Tripolar Nerve Cuff Electrode”, IEEE Transactions on Biomedical Engineering, vol. 39, no. 8, pp. 836-843, August 1989).
Nerve cuffs which use ring electrodes, which have been in use since the early 1970s, are illustrated in (for example) U.S. Pat. No. 8,615,294.